This invention relates to monolithic integrated circuit structures. More particularly, it is concerned with methods of fabricating bipolar transistors and resistors in monolithic integrated circuit structures.
Frequently there is a requirement for high frequency, low noise bipolar transistors in monolithic integrated circuit structure. In addition, the circuitry may require resistors having carefully controlled characteristics. Previously it has been difficult to obtain the desired control of critical emitter and base dimensions and resistivity profiles. Problems were also encountered in fabricating resistors, particularly high value resistors. Typically, resistors were formed simultaneously with the formation of the transistor base regions. Thus, the resistor dimensions were based upon the resistivity profile of the transistor base regions. Limitations in the precision obtainable with the photolithographic techniques employed in establishing the dimensions of the elements placed additional constraints on the ability to control device characteristics.